1. Field of the Invention
The present invention relates to manual air pumps for inflating, e.g., bicycle tires, and more particularly to dual-mode manual air pumps that may in one mode provide a very high volume of air per stroke and in another mode provide less volume of air at high pressure.
2. Description of the Related Art
Bicycle pumps, as mentioned in U.S. Pat. No. 5,676,529 to Hermansen et al. issued on Oct. 14, 1997, include two typical types: 1) big bore for high volume per stroke and low pressure for rapid inflation, yet high pressure operation is difficult to achieve; and 2) small bore for low volume per stroke and high pressure for inflating bicycle tires to high pressure. Hermansen et al. proposes a compact manual pump having selectable high volume and high pressure modes, wherein the pump in one mode provides a very high volume of air per pump stroke and in another mode provides less volume per stroke but enables the user to inflate to higher pressures. Nevertheless, in the output stroke shown in FIG. 4 of U.S. Pat. No. 5,676,529, air from the rear chamber defined between the outer tube 12 and the inner tube 24 must pass through the interior of the inner tube 24 before it enters a front chamber defined in the middle cylindrical tube 14. It is found that high pressure inflation is not reliable and unsatisfactory.
The present invention is intended to provide manual air pumps that mitigate and/or obviate the above problem.